The present invention relates to an apparatus for igniting a fuel/air mixture in the combustion chamber of a combustion engine, in particular a stationary gas engine, with at least one light source, an optical transmission apparatus and a coupling optic for focusing light into the combustion chamber.
Ignition apparatuses according to the preamble are known in the state of the art e.g. from DE 19911737 A1. Here, a laser beam guided in a light guide is coupled into the combustion chamber via a light element. Other approaches, such as e.g. U.S. Pat. No. 4,434,753 or U.S. Pat. No. 4,523,552, also provide that additives with high light absorption are additionally blown into the combustion chamber in the area of the supplied laser light. If these are struck by a triggered laser, they are heated. This leads to the ignition of the fuel/air mixture in the combustion chamber.
In the case of all laser ignition apparatuses, it is necessary in principle to provide by means of the laser the ignition energy required for ignition at the right time and in sufficient intensity. It is necessary to create an arrangement which withstands the permanent vibrations and the heat occurring around the combustion chamber. Furthermore, the manufacturing process of the ignition apparatus must be cost-favourable if it is to be used widely. These requirements are not, or only partly, fulfilled by the ignition apparatuses according to the preamble in the state of the art.
The object of the invention is therefore to create an apparatus according to the preamble in which the disadvantages of the state of the art are eliminated.
According to the invention, this is achieved in that at least one master light source is provided for the constant, preferably periodic, emission of untriggered, themselves non-flammable master light pulses and that the transmission apparatus includes at least one amplifier which is selectively triggerable and amplifies individual or groups of master light pulses to an energy level which is sufficient for igniting the fuel/air mixture.
It is therefore provided that master light pulses are produced constantly at a fixed frequency, guided via a transmission apparatus to the cylinder to be ignited in each case and introduced via a coupling optic into the combustion chamber of each cylinder. The energy of these master light pulses occurring constantly at fixed time intervals is alone not sufficient to ignite the fuel/air mixture. The ignition is triggered only by raising the energy level of individual master light pulses in a selectively triggerable amplifier, allocated to at least one cylinder, to the energy level necessary for ignition. This concept means that for several cylinders of an internal combustion engine, only one master light source is necessary, which emits light pulses at each ignition point of each cylinder via a suitable transmission apparatus. It is possible that all the cylinders of at least one combustion engine, and also that several amplifiers which are attached to a cylinder, are supplied with light pulses by at least one master light source. This means that the master light source can be arranged decentrally outside the vibration and heat area of the combustion engine.
A particularly favourable variant provides that the master light source is a laser. Favourable variants of these are constituted by the fact that the laser is axe2x80x94preferably diode-pumped and/or passively Q-switched and/or actively Q-switchedxe2x80x94solid-state laser. Among the solid-state lasers, Yb lasers and/or an Nd laserxe2x80x94preferably with Nd laser Cr4+ saturable absorberxe2x80x94represent favourable possibilities. Furthermore, these variants provide that the Nd laser is housed in a suitable host material, preferably Nd:YAG. As alternative host material, e.g. YLF, Vanadat can also be used. Furthermore, variants provide that the master light source is in microdisk form.
In order to achieve the required precision in fixing the time of ignition, it is favourable that the master light source emits light pulses or laser pulses with a repetition frequency of 1 to 25 kHzxe2x80x94preferably of 5 kHz. With regard to the pulse duration, it is favourable that the master light source emits light pulses or laser pulses with a pulse duration of 1 ns to 500 nsxe2x80x94preferably 100 ns to 300 ns (nanoseconds). With regard to the wavelength of the light emitted by the master light source, it is favourable that the wavelength of the light used is between 0.5 xcexcm (micrometres) and 20 xcexcm, preferably between 0.5 xcexcm and 5 xcexcm.
Favourable variants firstly provide that at least one amplifier of the transmission apparatus includes at least one light-amplifyingxe2x80x94preferably laser-activexe2x80x94light guidexe2x80x94preferably a flexible optical fibre. Secondly, favourable variants provide that at least one amplifier of the transmission apparatus includes at least one light-amplifying, preferably laser-active monolithic rod and/or at least one light-amplifying, preferably laser-active crystal wafer. In the case of both variants, it is provided according to the invention that the master light source is fixedly connected by glass fibre to several amplifiers, each allocated to at least one cylinder. In these amplifiers, there is accordingly triggered, within a defined time interval in the light-amplifying or laser-active medium, a quantity of energy which amplifies the next occurring master light pulse in energy-creating manner in such a way that an ignition of the fuel/air mixture is triggered in the combustion chamber of the cylinder allocated to the respective amplifier. The time of ignition is fixed by the triggering of the amplifier. As a result of this arrangement, the heat- and vibration-prone master light source can be arranged in a decentral location, while its pulses and the transported power can be distributed via single-mode fibers and/or thin multi-mode fibers. The master light source can thereby be decoupled from the cylinder mechanically (with regard to vibration and temperature), while the much more robust amplifiers (e.g. monolithic rod or crystal wafer) are seated against the cylinder.
In addition, it is particularly favourable that at least one amplifier amplifies the energy level of the light or laser pulses to 0.5 mJ (millijoules) to 10 mJxe2x80x94preferably 1 mJ to 5 mJ.
In the case of the use of a light-amplifying and/or laser-active, preferably flexible, optical fibre as an amplifier, it is particularly favourable that this has a section that is wound up, preferably in a coil shape. As a result the length, required for amplification, of the light-amplifying preferably flexible optical fibre can be fitted into a space which is small overall.
Favourable variants provide that at least one triggerable pump light source acting on at least one light-amplifying, preferably laser-active light guide and/or at least one light-amplifying preferably laser-active monolithic rod and/or at least one light-amplifying preferably laser-active crystal wafer is provided. The pump light source can be coupled longitudinally or transversally preferably via glass fibers to the light-amplifying or laser-active material.
Favourable versions provide that the pump light source is a semiconductor laser. Thus, e.g. quasi cw laser diodes with 800 nm wavelength can be used for Nd. Triggering takes place in these versions as required for each individual cylinder via the power supply e.g. of the quasi cw laser diodes, the emission duration of which is preferably between 150 and 200 ms.